This invention relates to a real-time electrical impedance tomography (EIT) system to provide for example blood flow imaging.
Tomography systems are described in GB-PS 2 119 520B or GB-PS 2 160 323B (U.S. Pat. No. 4,617,939 corresponding to both the content of the U.S. patent being incorporated hereinto by reference) or WO 89/09564 on which the present applicants/inventors are named as inventors, and in which the impedance imaging system consists of a data collection system (the data being measured potentials between pairs of electrodes in a series of contact electrodes attached around a human or animal body, and in which another pair is a "drive" pair between which currents are caused to flow) and an image reconstruction system. Frames of data could be collected serially by the data collection system at twenty-four frames per second but image construction could only be carried out at approximately one frame per second. Whilst this is not a disadvantage in extracting certain slowly changing physiological data there are other data requirements where it is necessary to produce images much more quickly--for example, when observing blood flow in the body during the cardiac cycle.
In order to produce a system able to produce images much more quickly two developments are required. Firstly, a much faster digital processor or computer in order to implement the image construction algorithm rapidly. Secondly, the data collected from the human body has to be improved in quality and in particular the noise level reduced. In the previous system noise level could be reduced by averaging signals over several seconds before constructing an image. However, averaging is not possible in a system running rapidly in real-time and therefore the noise level must be reduced by other means.